This invention relates to thin film transducers for recording and reading magnetic discontinuities on a magnetic recording medium and, in particular, to improved structures for and methods of manufacturing such thin film transducers or heads.
One approach to the design of thin films heads is described in my paper "Finite Element Analysis of the Vertical Multi-turn Thin Film Head", IEEE Transactions on Magnetics, Volume 14, Number 5, Sept. 1978, pages 506-508. As is described in that paper, it is customary to provide a close spacing (for example, a gap of the order of one micrometer) between upper and lower magnetic pole pieces at the read/write transducing gap of a thin film head. It is also advantageous to limit the "throat height" of the transducing gap to a relatively short distance (of the order of less than ten micro-meters).
The throat height of the head, which is defined as the distance from the pole tips to a point at which the two pole pieces begin to diverge from each other, normally is determined by grinding and lapping the pole tips to form an air bearing surface (ABS). The relatively small dimensions and tolerances associated with throat height require that precise indicies be provided for determining the location of the zero throat point or apex (the point at which the pole pieces diverge).
In the construction of earlier, physically larger, magnetic heads (see IBM Technical Disclosure Bulletin Volume 13, No. 3, Aug. 1970, pages 787-788, "Measuring Throat Gap Height of a Magnetic Head" by G. B. Flippen), it was possible to make use of a precise mechanical frame assembly and reference pins on a grinding fixture for indirectly locating the zero throat point, thereby controlling throat height. However, such techniques are not suitable for the extremely small dimensions encountered in thin film heads.
Where the small dimensions of thin film heads are involved, electrical resistance measurements of an active conductor pattern have been employed to determine the desired throat height (see U.S. Pat. No. 3,821,815 Abbott et al). The thickness of the conductor pattern had also been used to determine the gap length in that case. The gap length and the location of the zero throat point may also be determined by deposition of patterns of other materials. For example, one or more layers of insulating material (see U.S. Pat. No. 3,846,841 - Lazzari et al; U.S. Pat. No. 3,908,194 - Romankiw; U.S. Pat. No. 4,092,688 Nomura et. al; U.S. Pat. No. 4,190,872 Jones et al); one or more layers of conductive material (U.S. Pat. NO. 3,821,815 - Abbott et al noted above and U.S. Pat. No. 4,143,458 - Gibson) or combinations of insulating and conductive materials (U-S. reissue Pat. No. 29,326 - Lazzari et al) have been employed.
In at least some of the above-noted configurations (see U.S. Pat. No. 3,821,815 - Abbott et al and U.S. Pat. No. 4,092,688 - Nomura et al), the gap spacer material is electrically conductive and forms part of the energizing coil which extends between the pole pieces.
Despite the foregoing developments in the magnetic head arts, it has been found to be necessary to further improve the control of throat height and definition of the apex in the manufacture of thin film heads.
In accordance with one aspect of the present invention, a thin film magnetic transducer assembly comprises a substrate and a first magnetic pole piece disposed in a layered configuration relative to a surface of the substrate. At least one layer of electrically conductive material is disposed in a pattern which, in part, overlies the first magnetic pole piece. A second magnetic pole piece is disposed in a second layered configuration overlying the first pole piece and a portion of the electrically conductive material. The second pole piece is spaced from the first pole in a pole tip region to form a transducing gap of a first length and forms a back gap with the first pole piece in a back gap region. The pattern of conductive material includes first means adjacent the pole tip region for divergently spacing the first and second pole pieces apart by a distance greater than the transducing gap length in an apex region adjacent the pole tip region. The pattern also comprises second means outside the first and second pole pieces and having visible or optically detectable indicies in predetermined aligned relationship with the first means. The visible indicies extend at least to a target reference line in predetermined aligned relationship with the pole tip end of the pole pieces. The indicies are adapted for determining the location of the apex region relative to the desired pole tip ends.
These and other aspects of the present invention will be further described in the following specification in connection with the accompanying drawing .